I have 16 Bass Shakers in my wrap-around-couch. They work very well if I need to turn off the JL Audio 18"s for other's sake (daughter studing etc.)
Many manufactures have attempted planer speakers for a car. I don't know of any that actually have achieved status as I know of none who won SQ contests with them.
I'm pissed at myself because I can't remember who did a servo subwoofer for the car. It was to be equal the output of six 15" subs. Was it Phenoix Gold

I don't think it ever took off. I also know they made a smaller one in a tube.
Don't show EG that fan sub or he'll try to stick in his C5